Photochemical “Self-healing” pyrrole based treatment of CdS/CdTe photovoltaics

An improved post-deposition treatment for CdS/CdTe photovoltaic devices has been developed. Aqueous solutions containing pyrrole and sodium chloride provide a treatment of the CdTe surface when the device is illuminated with visible light. Evaporating gold metal on the CdTe surface completes the device structure. Comparison of the JV characteristics of the device treated with illumination to those not illuminated reveals a significant enhancement in device output. While most of the electronic properties (Jsc, FF, Rs and Rsh) are very similar the Voc for the treated sample is higher (circa 0.79 V versus 0.71 V) leading to a higher efficiency of 12.3% for the treated cell versus 11.0% for the untreated cell. The performance of this treatment is very much the same as that observed when the photochemically induced treatment employs aniline, the benefit of the herein described method is the decreased level of toxicity associated with pyrrole relative to that of aniline. Characterization of the CdTe surface with SEM does not reveal any noticeable features and could be interpreted as indicating that treatment leads to a very thin coating of material. The GIXRD data reveal the presence of elemental tellurium on the surface of the CdTe.